The present invention relates to isothermal chambers and more particularly, to isothermal chambers for use in fiber optic amplifiers.
Because of the loss associated with transmitting optical signals over long distances, ultra long haul (ULH) fiber optic telecommunications systems require amplification of the optical signal after a certain distance. Optical amplifiers allow the optical signals to be amplified without having to convert to the electrical domain. In submarine ULH systems with distances of about 7000 km, for example, these optical amplifiers are placed about every 30 to 50 km to compensate for signal attenuation and to boost signal strength. In an undersea environment, the optical amplifiers are housed together with other electrical and optical components in watertight housings (often referred to as repeaters), which are placed in line with the fiber optic cable.
In one type of optical amplifier, rare earth doped optical fiber is pumped with light at the wavelength of the rare earth dopant, thereby causing population inversion of the dopant. The population inversion causes a signal to propagate at a signal wavelength along the fiber, resulting in signal amplification. In some systems, for example, erbium doped fiber amplifiers (EDFAs) use erbium-doped fiber as the source of optical amplification. The erbium doped fiber is pumped with light energy usually coming from a laser, such as a 980 mn laser pump available from Lucent Technologies.
The length of erbium doped optical fiber can be stored in an erbium doped fiber module (EDFM) designed for storing a large quantity of xe2x80x9cloosexe2x80x9d fiber. The EDFM preferably protects the erbium doped fiber and maintains the erbium doped fiber within a certain temperature range for optimal performance. The temperature inside the EDFM (i.e., in the cavity or chamber where the erbium doped fiber lies) should remain substantially constant so that the output power of the amplifier remains constant or substantially constant. Previous and current designs of the EDFM do not provide an isothermal cavity or chamber for the erbium doped fiber. In fact, most chambers have gradients that are not tolerable with respect to keeping a constant output power. For example, the temperature variation across the cavity in some of these previous designs was in excess of 20xc2x0 C.
Accordingly, there is a need for a fiber optic tray with an isothermal chamber that is capable of keeping the temperature within the chamber substantially constant. There is also a need for an isothermal chamber capable of working in an undersea environment, for example, where the outside temperature is about 5xc2x0 F. and the chamber temperature is about 70xc2x0 F.
In accordance with one aspect of the present invention, an isothermal fiber optic tray comprises a thermally conductive inner structure providing a substantially isothermal cavity and an insulating outer structure positioned adjacent first and second sides of the thermally conductive inner structure.
In accordance with another aspect of the present invention, a fiber module comprises a housing, first and second conducting plates positioned within the housing to define a substantially isothermal cavity for receiving the optical fiber, and first and second insulation sections positioned within the housing adjacent the respective conducting plates. The fiber module also comprises first and second heaters positioned between the respective conducting plates and insulation sections.